Automatic door operating systems are commonly used in vehicles such as passenger transit buses and rail cars, for example. The door or doors of such systems have a pneumatic sensing edge connected by a gas conduit or hose to a pressure wave switch included in an electrical control circuit for the door operating system. When the sensing edge makes momentary contact with an object on closure of the door, a pressure pulse or wave is produced that propagates through the gas conduit to actuate the switch. The switch then provides a control signal energizing an operator of a door opening mechanism to open the door automatically.
Mechanical pressure wave switches are currently being used for passenger door obstruction sensing. Such conventional mechanical pressure wave switches typically use two mechanical metallic contacts that are subject to oxidation and other environmental contamination that can reduce the reliability or sensitivity of the switches, as well as creating a failure condition. The mechanical contact components of mechanical pressure wave switches have no self-cleaning capabilities such as contact wiping. Moreover, the mechanical contacts pass very low current (approximately 12-18 milliamps) which is not enough to keep these mechanical contacts clean.